Abstract
Packed bed reactors have been widely applied in industrial production, such as for catalytic hydrogenation. Numerical simulations are essential for the design and scale-up of packed beds, especially direct numerical simulation (DNS) methods, such as the lattice-Boltzmann method (LBM), which are the focus of future researches. However, the large density difference between gas and liquid in packed beds often leads to numerical instability near phase interface when using LBM. In this paper, a lattice-Boltzmann (LB) model based on diffuse-interface phase-field is employed to simulate bubble rising in complex channels saturated with liquid, while the numerical problems caused by large liquid-to-gas density ratio are solved. Among them, the channel boundaries are constructed with regularly arranged circles and semicircles, and the bubbles pass through the channels accompanied by deformation, breakup, and coalescence behaviors. The phase-field LB model is found to exhibit good numerical stability and accuracy in handing the problem of the bubbles rising through the high-density liquid. The effects of channel structures, gas-liquid physical properties, and operating conditions on bubble deformation, motion velocity, and drag coefficient are simulated in detail. Moreover, different flow patterns are distinguished according to bubble behavior and are found to be associated with channel structure parameters, gravity Reynolds number (ReGr), and Eötvös number (Eo).
Highlights
Packed bed reactors have the advantages of simple structure, convenient operation, low operating cost, good heat, and mass transfer performance, and have been widely used in industrial processes such as catalytic hydrogenation [1], oxidation reaction [2], nitrification reaction [3], and wastewater treatment [4], among others
The numerical studies on two-dimensional bubble rising in complex channels saturated with liquid at large density ratios within a wide range of gravity Reynolds numbers and Eötvös numbers have been implemented using phase-field LB model
The present LB model is tested through three aspects of Laplace law, bubble deformation, and mass conservation, and it has been proven to have good stability, accuracy, and conservation from both qualitative and quantitative perspectives
Summary
Packed bed reactors have the advantages of simple structure, convenient operation, low operating cost, good heat, and mass transfer performance, and have been widely used in industrial processes such as catalytic hydrogenation [1], oxidation reaction [2], nitrification reaction [3], and wastewater treatment [4], among others. The detailed dynamics of the dispersed phase and the complicated topological evolution of the gas-liquid interface are difficult to fully understand through experiments or numerical simulations on the reactor scale. The direct numerical simulation (DNS) provides us with a promising solution, in which the lattice-Boltzmann method (LBM) has attracted more and more attention due to its simple computation and clear physical background. The density ratios of liquid to gas in the Processes 2020, 8, 1608; doi:10.3390/pr8121608 www.mdpi.com/journal/processes
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